This invention relates to an acceptor for money items such as coins and banknotes and has particular but not exclusive application to a multi-denomination acceptor.
Coin and banknote acceptors are well known. One example of a coin acceptor is described in our GB-A-2 169 429. The acceptor includes a coin rundown path along which coins pass through a coin sensing station at which sensor coils perform a series of inductive tests on the coins in order to develop coin parameter signals which are indicative of the material and metallic content of the coin under test. The coin parameter signals are digitised and compared with stored coin data by means of a microcontroller to determine the acceptability or otherwise of the test coin. If the coin is found to be acceptable, the microcontroller operates an accept gate so that the coin is directed to an accept path. Otherwise, the accept gate remains inoperative and the coin is directed to a reject path.
In banknote validators, sensors detect characteristics of the banknote. For example, optical detectors can be used to detect the geometrical size of the banknote, its spectral response to a light source in transmission or reflection, or the presence of magnetic printing ink can be detected with an appropriate sensor. The parameter signals thus developed are digitised and compared with stored values in a similar way to the previously described prior art coin acceptor. The acceptability of the banknote is determined on the basis of the results of the comparison.
When a number of coins or banknotes of the same denomination are passed through an acceptor, successive values of coin parameter data are thus developed. When the distribution of the values of these signals are plotted as a graph, the result is a bell curve, with a central peak and tails on opposite sides. The shape of the graph may typically although not necessarily be Gaussian.
The distribution illustrates that for a money item, such as a coin or banknote of a particular denomination, the most probable value of the corresponding parameter signal lies at the peak of the bell curve, with a decreasing probability to either side. In prior coin and banknote validators, data is stored in a memory, corresponding to acceptable ranges of parameter signal for a particular denomination. The acceptor thus compares the value for a coin or banknote under test with the stored data to determine authenticity. The data may define windows in terms of upper and lower limit values, or as a mean value and a standard deviation, such that the window comprises a predetermined number of standard deviations about the mean. By making the stored windows narrow, an increased discrimination is provided between true money items and frauds. However, if the windows are made too narrow, the rejection rate of true money items increases, disadvantageously. The width of the windows is thus selected as a compromise between these two factors. Attempts to defraud coin or banknote validators typically involve the manufacture of facsimile coins or banknotes which cause the accept to produce parameter signals which lie within the stored acceptance windows.
In U.S. Pat. No. 5,355,989, a coin acceptor is described which switches from using a first normal acceptance window for a true coin, to a second narrower window when a coin parameter signal produced by testing a coin, falls in a region of the normal window for the true coin, corresponding to a low acceptance probability region for the coin concerned. A group of fraudulent coins may all have similar characteristics and they may cause the validator to produce to produce parameter signals which lie within the normal window, but the parameter signals consistently have a value which is not centered on the high probability peak region of the window associated with the true coin but instead are centered on the lower probability tail regions of the bell curve distribution within the normal window. When the parameter signal falls within this low probability region, the second narrower window is then used for the next tested coin. If the next coin has a parameter falling in the narrower window it is a true coin but if not, it is a fraud which should be rejected. This approach seeks to prevent frauds carried out by the use of coins of a particular low value denomination, from a foreign currency set, with characteristics that correspond but are not exactly the same as a high value coin of the currency set that the acceptor is designed to accept. It will be understood that the foreign denomination coins exhibit their own generally Gaussian distribution of parameter signals, and if the low probability or tail region of this distribution partially overlaps a corresponding region of the distribution for the true coin that the acceptor is designed to accept, then the low value foreign coins will sometimes be accepted as true coins. However, significant problems remain. In the arrangement disclosed in U.S. Pat. No. 5,355,989, when a true coin is inserted, the system switches back from the second narrower window to the first normal acceptance window.
If the next coin inserted is a foreign currency coin, if it has a parameter signal within the normal acceptance window, it will be accepted although the system will then switch to the second narrower window for the next coin under test. If the next coin tested is a true coin, it will be accepted and the system will switch back to the first window. U.S. Pat. No. 5,355,989 considers the possibility of counting groups of n coins before making the switch between the windows. Thus, with the prior system, it is possible to obtain acceptance of a significant number of foreign currency coins by alternating them with true coins either individually or in equal numbered groups of n coins. A further disadvantage is that the system is very slow because the foreign coins do not all produce an acceptance and so when a fraudster is attempting to use foreign coins they may be rejected a number of times of falling outside of the first relatively wide acceptance window. However, the prior validator takes no account of the fraud attempt and will only respond when a fraudulent coin is in fact accepted.
The present invention seeks to overcome these problems. In accordance with the invention from a first aspect there is provided a money item acceptor comprising: a signal source to produce a money item parameter signal as a function of a sensed characteristic of a money item, a store to provide data corresponding to a normal acceptance range of values of the parameter signal for a money item of a particular denomination, the range including relatively high and low acceptance probability regions wherein the value of a parameter signal corresponds to a relatively high or low probability of an occurrence of sensed money item of said particular denomination, and a processor to determine when an occurrence of the parameter signal corresponding to a first money item adopts a predetermined value relationship, and in response thereto, to compare the value of a subsequent occurrence of the parameter signal corresponding to a second money item with data corresponding to a restricted acceptance range as compared with the normal acceptance range, and to provide an output corresponding to acceptability of the second money item if the second occurrence of the parameter signal falls within restricted acceptance range, wherein said predetermined value relationship occurs when the parameter signal corresponding to the first money item has a value within a predetermined security barrier range outside of the normal acceptance range.
In accordance with the invention, the predetermined security barrier range can be generally aligned with the peak of the distribution for the fraudulent coin so that even if the fraudulent coin produces a parameter signal outside of the normal acceptance range, the existence of the fraud attempt is detected and the acceptor switches to the restricted acceptance range to reduce the risk of fraud.
The invention further includes a corresponding method of detecting fraudulent coins.
In a second aspect, the invention provides a money item acceptor comprising: a signal source to produce a money item parameter signal as a function of a sensed characteristic of a money item, a store to provide data corresponding to a normal acceptance range of values of the parameter signal for a money item of a particular denomination, the range including relatively high and low acceptance probability regions wherein the value of a parameter signal corresponds to a relatively high or low probability of an occurrence of sensed money item of said particular denomination, and a processor to determine when an occurrence of the parameter signal corresponding to a first money item adopts a predetermined value relationship with the low acceptance probability region, and in response thereto, to compare the value of a subsequent occurrence of the parameter signal corresponding to a second money item with data corresponding to a restricted acceptance range as compared with the normal acceptance range, and to provide an output corresponding to acceptability of the second money item if the second occurrence of the parameter signal falls in the restricted acceptance range, said processor being operable to compare a first predetermined number of subsequent occurrences of the parameter signal with the restricted acceptance range, and if all of them correspond to acceptable money items, to revert to the normal acceptance range, wherein when using the normal range, the restricted acceptance range is selected in response to a second pre-selected number of occurrences of the parameter signal, smaller than said first predetermined number, adopting said predetermined value relationship.
By making the second pre-selected number smaller than the first pre-determined number, the discrimination against fraudulent coins is substantially improved. For example, only a single occurrence of a potentially fraudulent coin can trigger use of the restricted acceptance range and then, a larger number of occurrences of true coins falling within the restricted acceptance range need to occur before switching back to the normal acceptance range. Thus, if the fraudster repeatedly attempts to defraud the acceptor with fraudulent coins, each such attempt may trigger the use of the restricted acceptance range which is then used for a number of times so as to block subsequent fraud attempts. The acceptor is however responsive to each new fraud attempt thereby reducing the risk of acceptance of further fraudulent coins.
The processor may be operable to compare a predetermined number of subsequent occurrences of the parameter of the parameter signal with said restricted acceptance range, and if said predetermined number all correspond to acceptable money items, thereafter, to revert to the normal acceptance range.
The processor may further operate to compare any subsequent occurrences of the parameter signal with said restricted acceptance range for a predetermined time and then to revert to the normal acceptance range.
The signal source may be operable to produce a plurality of individual money item parameter signals each as a function of a respective different characteristic of a sensed money item, and the store may be configured to provide window data for normal acceptance ranges of values of the parameter signals individually for a money item of a particular denomination.
The processor may be operative to compare the first occurrence of each parameter signal individually with a corresponding one of said normal acceptance ranges, and to compare a subsequent occurrence of each of the different parameter signals with a corresponding restricted acceptance range for each parameter signal, in response to any one of the first occurrences of the parameter signals having a predetermined value relationship with the low acceptance probability region of its corresponding normal acceptance range.
Alternatively, the processor may be operative to compare the first occurrence of each parameter signal individually with a corresponding one of said normal acceptance ranges, and to compare a subsequent occurrence of each of the different parameter signals with a corresponding restricted acceptance range for each parameter signal selectively in response to the corresponding one of the first occurrences of the parameter signals having a predetermined value relationship with the low acceptance probability region of its normal acceptance range.
The acceptor according to the invention may be configured for use with coins, banknotes or other money items.